APPENDIX ON THE ELECTRICAL CONDUCTIVITY 

 OF EGG-ALBUMIN 1 



ALTHOUGH it is not possible to obtain exact measurements of the 

 electrical conductivity of protoplasm, it in all probability does not differ 

 widely from that of such colloidal substances as egg-albumin containing 

 corresponding percentages of water. It is also of interest to determine 

 whether the decreased resistance following the death of the protoplasm 

 is also shown when egg-albumin coagulates. 



Using a battery of two standard cells it was at once seen that electro- 

 lytic decomposition occurred ; bubbles of gas appearing on the electrodes, 

 and the neighbourhood of the kathode becoming alkaline, and that of the 

 anode acid. The resistance offered by an electrolyte depends in part 

 upon the back electromotive force generated by the electrolytic products. 

 In this case a voltameter, thrown into circuit by a key breaking the main 

 current at the same instant, registered a maximum temporary deflection 

 of 0-6 volt. The difference of potential due to the electrolysis is probably 

 even higher than this, for a cell of 1-4 volts gave an extremely feeble 

 current through two centimetre cubes of egg-albumin. 



To obtain the true resistance the differential method must be em- 

 ployed, by using the apparatus shown in Fig. 16, in which the current 

 can either be sent from the second to the third or from the first to the 

 third electrode, that is, through a measured additional length of egg- 

 albumin. The increase in the resistance gives the amount due to this 

 additional length apart from any polarization effect. After each obser- 

 vation it is advisable to join up the electrodes for a short time, and 

 then take an additional one with the current reversed. The resistance 

 is most conveniently measured by the interpolation of known values 

 in place of the egg-albumin, until the sensitive needle galvanometer used 

 gives the same deflection. In addition, it need only be remarked that 

 platinum electrodes must be used, and that these should be in the form 

 of circular transverse plates which just fit into the tube, and are pre- 

 ferably insulated on the connected side. 



Working in this manner values were obtained for the absolute resistance 



1 This appendix was written after the foregoing paper had been read to the Royal Society. 



